Black Magic Exploitation

CTF's, Exploits, and Black Magic

QueerCon 2016 ~ QC13 Soundcheck: Stego

For those that don’t know - QueerCon is an LGBTQ subgroup of DefCon, the worlds largest hacking convention in the world. Every year they have 1-3 challenges a year. This was the first and can be located at the QueerCon Contest Link where I was able to win a QueerCon 13 Badge for this years DefCon.

Contest Details

A beat to make you dance!

Do you like music? Have a good ear? Check out this hot beat from Stemodity. Get prizes!

Listen closely! Good luck!

Stemodity - Crypto
Think you have solved the puzzle? Care to find out? 

Send your find to answer (at) queercon (dot) org; and we will let you know.   

Give up? Stay tuned for clues! They will be posted around in various places; such as on our Mobile App or Facebook page.  

Looks like we were given a song from Sound cloud. Given the clues, looks like there is some kind of hidden message in the song. Because the contest hinted:

Listen closely! Good luck!

I turned on the song for the next four hours while solving this puzzle to make sure it got stuck in my head.

Like any stego expert I downloaded the full song from SoundCloud and looked at its metadata using exiftool which I saved here

Looking at the metadata

As you can see, we got nothing from here. Referencing a few audio writeups, I thought I should try looking at its spectrogram. Using sox, the swiss army knife for audio manipulation, I made a spectrogram for the song. I did have some issues using sox with mp3 but I referenced this super user post to convert it to a wav file or allow sox to run with mp3’s. After which I ran spectrogram command:

Making the spectrogram

As you can see there are few areas where the signal magnitude values (dBFS) are super high (where its yellow). Next step is to isolate each of these areas using Sox. The command I used was:

 sox <audio file> -n trim <time> <duration> spectrogram -o <ouput file>

sox Crypto\ [QueerCon13].mp3 -n trim 1 1 spectrogram -o spectrogram-1-1.png

sox Crypto\ [QueerCon13].mp3 -n trim 10 5 spectrogram -o spectrogram-10-5.png

sox Crypto\ [QueerCon13].mp3 -n trim 65 5 spectrogram -o spectrogram-65-5.png

sox Crypto\ [QueerCon13].mp3 -n trim 110 5 spectrogram -o spectrogram-110-5.png

sox Crypto\ [QueerCon13].mp3 -n trim 169 5 spectrogram -o spectrogram-169-5.png

The results were:


This was amazingly hard to decipher so I pulled up Sonic Visualizer which lets me see a live spectrogram. It also has more room for users to zoom in and out in the spectrogram. Usage: Open Audio File -> Shift + G (Spectrogram layer) -> Double Click Bottom Right Visible Range scale to adjust to according dBFS level. This were the results:


My deciphering got me to think this text was:


At this point in time I wasted a whole bunch time with ciphers at such as caesars, vigenere…etc. Don’t get me wrong I know how most of these work, why rebuild the wheel? I didn’t really find anything here for a while. I tried other approaches such as looking at the metadata of the image that came along with the contest, but that didn’t give me anything either. I even listened to the song like 50 more times to see if I missed anything. You can say I wasted like four hours here:


Thinking I missed something back at, I tried the ciphers again and eventually got a hit with the playfair cipher. NOTE: MAKE SURE YOU CHANGE TO DECRYPT INSTEAD OF ENCRYPT THE FIRST TIME TO MAKE SURE YOU DON’T WASTE FOUR HOURS TRYING OTHER CIPHERS. As such I input the text we had SALD LESUW TNDI UIKX NPTUC and I got:


Something was obviously wrong with the first word so I looked back at the spectrograms and realized the “LD” in “SALD” was actually a “13” to make “SA13”. This translates the final ciphertext to:


This was the 13th year for QueerCon so this made sense. I emailed which resulted in no response for a couple weeks. After which I saw on the QueerCon Facebook page that many people didn’t get replies. I emailed one of the other QC ubers and was finally able to confirm I got the right answer along with a cool QC badge!

QueerCon Badge
*Photo from hackaday by Eric Evenchick*

If you want a review of this year’s badge feel free to head to Thanks again QueerCon for the awesome and fun challenge